Contraction of blood vessels and observations on the circulation in the transparent chamber in the rabbit's ear.код для вставкиСкачать
CONTRACTION O F BLOOD VESSELS AND OBSERVATIONS ON T H E CIRCTJLATION I N T H E TRANSPARENT CHAMBER I N THE RABBIT'S EAR J . C. SANDISON Laboratory of A n a t o m y , Y e d i c a l School, University of Pennsylvania, Philadelphia, Pennsylvania SEVEN FIGUR.EB The contractility of small blood vessels is a subject which has been studied in the living by a number of investigators during the past sixty years. Before Stricker ('65) saw the phenomenon of independent contraction of capillaries in the nictitating membrane of the frog, these vessels were thought to respond to circulatory changes in a passive manner only, the flow of blood through them being regulated entirely by the contraction and dilatation of vessels surrounded by muscle cells. Lister ('58) had noticed a dilatation of capillaries in inflammation. The further studies of Golubew ('69), Rouget ( '73), Tarchanoff ( '74), Roy and Brown ( '79), Steinach and Kahn ('03), and many others, established the fact that capillaries are contractile as well as elastic. Most of these observers studied the capillaries of amphibians and obtained contractions by using mechanical, electrical, or chemical stimuli. Renewed interest in capillary contractility has recently been aroused by the studies of Vimtrup ( '23)' working under Krogh ( '22). Vimtrup made a careful study of the adventitial cells of capillaries which were first described by Rouget, and which he termed 'Rouget' cells. Using the transparent tails of living amblystoma larvae, he observed definite contraction of capillaries without any special stimulns, and 105 THE ANATOMICAL XEC'OXD, TOT.. 5 4 , N O . 2 106 J. C. SANDISON described it as being inaugurated by the contraction of Rouget cells. Parker ( ’ 2 3 ) and Federighi ( ’28) described, in certain invertebrates, the active contraction of endothelium of capillaries on which no adventitial cells could be seen. E. R. and E. L. Clark (’25), repeating Vimtrup’s studies on larvae of Amblystoma and of Anurans, found active contraction of capillary endothelium, but failed to corroborate Vimtrup as regards thc part played by the ‘Rouget’ cells, since they observed contraction of capillaries on which there were no ‘Rouget’ cells, and since, in capillaries on which sparsely distributed ‘ Rouget ’ cells were present, the inauguration of the contraction occtirred much more often away from the ‘Rouget’ cells than in their immediate neighborhood. Moreover, they noted that the endothelium contracted away from the ‘Rouget’ cell, leaving a clear space between. It is, then, clearly established that in Amphibia capillary endothelium possesses the property of active contractility, and that capillary contraction plays an important rale in regulating blood flow. For the mammal, until recently, nothing has been definitely known, in spite of a large number of studies by Hooker, Krogh, Rich, Hill, Florey and Carleton, and others. The reason for this uncertainty has been the unavailability of any region in a mammal in which the smallest blood vessels could be seen with sufficient clearness in the living under normal conditions. This need has been supplied by the artificial production of a tissue so thin and transparent that the individual cells of the walls of arteries, veins, and capillaries may be seen clearly with the highest microscopic lenses, and in which prolonged studies may be made of the same vessel similar to those carried out in the tail fins of amphibian larvae. The method developed in this laboratory, under the direction of Dr. Eliot R. Clark, consists of the introduction into a hole made in the ear of the rabbit of a thin, transparent, double-walled chamber with its sides open to the deeper tissues of the ear, and into which new blood vessels and connective tissue grow, forming a tissue which is per- CONTRACTION OF BLOOD VESSELS 107 manent and which is essentially similar to the subcutaneous tissue of the ear (Sandison, '24, '28 ; Clark, Kirby-Smith, Rex, and Williams, '30). As described in a previous paper (Sandison, 'as), the newly formed blood vessels undergo a complete differentiation into arteries, arterioles, capillaries, and veins. Recently (Clark et al., '31), a description has been given of the ingrowth and differentiation of blood vessels in sixty standard chambers under controlled and approximately uniform conditions, with a correlated study of the circulation, and the subsequent changes in the vascular pattern over a period of months (over a year in several cases). The studies to be described here were made on chambers constructed entirely of kodaloid (Sandison, '28). The vessels were all new ones which had formed by ingrowth into the chamber from the subcutaneous vessels of the ear, and the observations were carried out largely on a chamber in which the vessels were from two to four and one-half months old. The major purpose of the study was to find out, if possible, just what elements of the minute vessels are responsible for the regulation of flow through the capillaries, whether the capillary endothelium is contractile, what part the adventitial or 'Rouget' cells may play, to what extent the flow is regulated by the smooth-muscle cells, and what other factors may be concerned with the capillary circulation. It should be mentioned that nerves were not seen in the present observations on the new vessels, and it was uncertain whether they were present or not. However, important as this question may be from many standpoints, it does not seriously affect the primary object of this study. A preliminary account of these observations was presented before the Physiological Society of Philadelphia, May, 1928. OBSERVATIONS ON CONTRACTION It was early noted that, in a well-developed plexus, there were frequent changes in the circulation; periods of active flow alternating with periods of marked slowing or even of 108 J. C. SANDISON actual stasis. Careful study showed that the circulation in any given plexus of vessels changes in an almost rhythmical manner.l On the average, about twice in each minute, the free, active flow of blood is interrupted by a slowing or stasis of a few seconds duration. Examination of the various parts of the system to discover the factors responsible for this periodic slowing brought out certain interesting facts. It became clear that it is the contraction and relaxation of the smooth-muscle cells of the arteries and arterioles which cause the changes in the circulation. The adventitial or 'Rouget' cells, which are present in abundance on the precapillaries, play no part whatsoever in the contraction, and the endothelium of the capillaries displays a power of contractility so slight that it is not a factor in the regulation of the blood flow. The contraction sometimes appears first in the main artery of the ear, which narrows markedly, and may extend as a wave along the arteries and their branches and the arterioles until the last smooth-muscle cell is reached, three o r four seconds being taken up ill the passage of the wave from large artery t o small arteriole. The narrowing in the different parts of the arteries may be partial or it may be sufficient to block completely the flow of blood. Contractions of the smooth-muscle cells around the arterioles do not occur simultaneously in all arterioles, and as a result of this alternating contraction, the blood may flow first in one and then in the opposite direction in the same vessel (fig. 1). The smoothmnscle cells on the larger arteries may remain contracted for long periods of time under certain conditions, while the musClark and Clark ( '32) havr made observations on the liviiig preformed blood vessels, using the 'preformed tissue' chamber (Clark et al., 'SO), in ' ~ ~ h i cthe h niain artery of the ear is retained and a thin, transparent area about 1.5 em. in diameter, iiiclurling the preformed arteries, veins, and capillaries. Thcy dcscribc the iiornial occurreiice of spontaneous rhythmic contractions of arteries, involving the main artery of the ear, down t o smaller and smaller branches, and fiiid that the different arteries and parts of the same artery each contract a t a different tempo and t h a t the periodic contractions have a profound influence on the distribution of blood t o different arras and on the direction of flow in different vesvls. CONTRACTION O F BLOOD VESSELS 109 cle cells on the arterioles rarely remain contracted f o r more than a few seconds. That it is the smooth-muscle cell which is almost exclusively responsible for the contraction of vessels comes out most strikingly from a study of the smaller arterioles and capillaries. In the arterioles the continuous sheet of smoothmuscle cells is succeeded by muscle cells in groups, and these in turn by pairs, and finally by isolated single cells. They can be readily seen, especially with the oil-immersion lens, as small round structures outside of and encircling the endothelium. They can be distinguished easily from the adventitial cells which lie longitudinally along the vessel, and which I I I I C D c A Fig. 1 Camera-lucida tracings, showing the size of the lumen of a n artery (1) and its branch ( 2 ) , in CiEerent phases of dilatation and contraction. A, both 1 and 2 dilated; B, 1 partially, 2 completely contracted; C, 1 completely, 2 partially contracted; D, both 1 and 2 completely contracted. x 310. are larger in cross section. If such an area is watched it will be seen that the arterioles contract at the places where the smooth-muscle cells are present, and that the vessels beyond the last cell narrow only to a very slight extent, if at all. It is most fascinating t o watch the contraction of a single isolated smooth-muscle cell on an arteriole (fig. 2 ) . When undergoing a contraction, it causes a rapid narrowing so that, in the course of two o r three seconds, the lumen may be so constricted that no blood cell can pass. It remains contracted for three or four seconds and rather suddenly relaxes, the relaxation being immediately followed by a rush of blood through the vessel. It remains relaxed for periods of time varying from ten seconds to a minute, and then contracts 110 J. C. SANDISON again. The smooth-muscle cell does not always constrict the lumen completely, for it may contract only partially and narrow the lumen without obliterating it. The periods of relaxation are definitely longer after the partial contraction. While these definite contractions are occurring in the smooth-muscle cells, which regulate the flow of blood, there are only such general changes in the capillaries as can clearly be explained on the basis of elasticity and of outside or inside pressure. Following the shutting off of the blood flow, there may be a slight general narrowing of the capillary, to be followed by a slight widening when active circulat#ion is reI . I . ~ I I I . 1 ~ 1 1 . I . . . I . . . . I I . . . . . I . . . , . / . . . . . I I I I . . l . . . I . I . . . . . 1 9.08 A M . 9.09 9:11 9:lO 9:12 / v v \ A A I . . . . I I . I . . I I . ~ . . . I . . . . . I . . . I . I . I . . . I . . . . I I . I . . . I I , . I . I . . . I . I 9:13 I . . . . .I 9 I8 9;14 . I . . . 1 .....I 919 9:15 . . . . . I . . . . . 9 20 9.16 I 9.17 . , . . , I . , , . . , . , . , -j 9 21 9 22 Fig. 2 Diagram showing the degree and rate of changes in caliber of an artrriole following coiltraction of a single muscle cell which almost completely surrounded the arteriole. The contraction periods of this cell occurred at the same time as did the rhythmical ones of the arteries within the whole chamber. sumed. Rut these changes are obviously secondary to the contraction and relaxation of the smooth-muscle cell on the arteriole. At times there has been observed a complete emptying of an extensive capillary plexus, coincident with a reduction in blood flow, and occurring simultaneously with the contraction of the large supplying artery. This simulated capillary contraction, but was found to be due to the pressure exerted on the tissue by the thin, elastic celluloid cover of the chamber, for pressure over the area with a fine glass rod produced an identical picture. Evidently the widening of the arteries raises the cover slightly, permitting easy circulation through the capillaries, while the contraction of arteries CONTRACTION O F BLOOD VESSELS 111 allows the cover to spring back and compress the capillaries, particularly over the tables. This was further proved by constructing chambers in which the covering celluloid was cemented in places to the tables to make it rigid. In such chambers the capillaries did not show this peculiar type of emptying. The circulation is markedly influenced by the development of muscle cells on the newly formed capillaries as they become transformed into arterioles. Changes in caliber were observed in the same vessels both before and after the appearance of muscle cells on their walls. It was found that before the development of these cells the narrowing of such vessels was always very slight, involved the whole vessel uniformly, and followed the rhythmic contraction of the main artery just described. After the appearance of muscle cells, however, the same vessels were seen to display localized narrowings, and such constrictions always occurred in the region of the newly developed smooth-muscle cells. OBSERVATIONS ON THE CIRCULATION The manner in which blood flows through vessels and the behavior of the blood cells in the normal blood stream were observed and described many years ago by numerous investigators and only a few new observations have been made on the circulation as studied in the rabbit's ear. However, since most of the previous work on this subject has been carried out on the mesentery of mammals where one is limited to short observation periods, it is of interest to restudy the problem in the transparent chamber, where the same blood vessels may be seen from day to day for months, and the circulatory changes in them observed during both their early formation and their subsequent adult growth. The different rates of flow in various kinds of vessels at different stages of growth, together with the causes for these variations, have already been discussed and partly analyzed (Sandison, '28). One sees in the blood current in the rabbit's ear the well-known axial stream of cells, and the compara- 112 J. 0. SANDISON tively narrow, clear, plasma layer, or 'randzone,' which surrounds this rapidly moving central core. The throwing off of the leukocytes into the peripheral layer and their slow rolling motion along the vessel wall is also a phenomenon which is readily seen. I n this study it has been observed that the presence of the clear peripheral stream is dependent upon the rate of flow: it is widest when the blood is flowing rapidly, and occurs chiefly in the arteries and arterioles, except when these vessels are so constricted that the single blood cells are squeezed in passing through. When the circulation slows down or stops, during a period of contraction of the arteries, this peripheral layer is absent in all vessels. At such times the erythrocytes and leukocytes are no longer limited to the axial stream, but wander a t random; or they may settle to the dependent part of the lumen, leaving only a clear layer of plasma above. During a period of stasis, which may last for several seconds or minutes, this sedimentation of blood cells may be quite noticeable, particularly in the larger vessels. Then, too, an uneven mixture of cells with plasma has been observed during a period of sluggish or irregular flow of blood through the capillaries-a condition which results in part from an irregular contraction of first one arteriole and then another. This independent contraction of arterioles (i.e., one vessel closed at the same time another is open) causes blood to be fed to the veins through the capillaries and venules in the form of a broken stream. An uneven mixture may also occur within an arteriole or an artery itself as a result of contractions occurring at intervals along their walls, leaving dilated portions of the vessel in which clumps of cells collect (Art. G, fig. 5). When such contracted regions again dilate and the circulation is resumed, the clumps of cells pass on without mixing evenly again until they reach the larger lumen of the venules. I n this connection the work of Landis ('26) is of interest. He has been able to measure capillary pressures during capillary stasis in the frog's mesentery and to watch the flow of plasma through the endo- CONTRACTION O F BLOOD VESSELS 113 thelium as indicated by the passage of injected dye. He finds that wherever such a flow is present there is a considerable change in the proportion of blood cells and plasma within the lumen. The phenomenon of ‘plasma skimming,’ a term introduced by Krogh (?la), and that of leukocyte skimming may be exhibited in various ways. The former is seen mainly in partially contracted vessels or in capillaries which are cross connections between the main path of the circulation and which, even though dilated, have no circulation on account of equal pressures at their two ends; it may be seen also in blind-ending, new-growing tips. Not infrequently vessels containing skimmed plasma, i.e., plasma without erythrocytes, are loaded with leukocytes which, along with the plasma, have been skimmed off from the main circulation. In fact, leukocyte skimming may be seen in practically any uncontracted vessel in which the circulation has temporarily ceased, but which remains connected with other circulating vessels . The following observation on platelet skimming was also made: in a single, very narrow capillary loop, whose two ends were connected to a large circulating vessel, plasma flowed at all times, as was indicated by the passing of the smallest blood platelets. For many minutes only platelets would pass. It was interesting to note that with an increase of blood supply through the large vessel, erythrocytes would be forced through the narrow loop. With a very rapid rate in the larger vessel, accompanied supposedly by an increase in blood pressure, even the largest leukocytes were forced through the capillary, although its entrance was so constricted that the cells, in passing, were forced out into very long and narrow forms. Plasma skimming is not confined to capillaries, since it has been seen in arterioles which are constricted almost completely at their proximal end and dilated along the remainder of their course, the dilated portion containing only a single blood cell here and there. Such plasma skimming in an arte- 114 J. C. SANDISON riole is a rather complicated condition, and certain factors must be present for its occurrence. I n the first place, the flow of blood through any arteriole is dependent upon: the degree of dilatation and the rate of blood flow in the artery which supplies it, the pressures in the capillary bed which the arteriole itself supplies, the size of its entrance, and the caliber of its entire lumen. Plasma alone will enter the arteriole when its entire lumen or merely the lumen at its entrance, is constricted to a size much smaller than the blood cells, and when the pressure of its arterial supply is not sufficient to force cells through the constricted opening. When, as indicated by the passage of platelets, plasma flows through a vessel under these conditions, an occasional cell may enter it, but if both the pressure in the capillary plexus beyond it and that at its entrance become equalized (a condition which may result from the passage of blood through another arteriole into the same plexus of capillaries) blood flow will cease in this vessel, the cells will be drawn off, and true plasma skimming will usually follow. Krogh ( ’22), in studying the frog’s web and tongue, saw a washing away of the erythrocytes, when he stimulated a portion of a small artery branching from a larger vessel almost to the point of complete contraction. He stated that the current of blood through the small artery seemed t o cease altogether, and that at the same time the erythrocytes were washed out from the corresponding capillaries. I n the rabbit’s ear one also sees that the cells are washed away from a capillary bed, following contraction of the arterioles o r arteries, but there still may be a continuation of the flow of the plasma containing platelets only. In regard to the capillaries, however, this same plasma skimming may occur as the result of another factor, i.e., the reversal of flow in an arteriole-a phenomenon which occasionally takes place during a short period of stasis in the artery. I n this case, the blood cells are drained out of the capillary plexus in the absence of circulation. It will be noted, therefore, that two types of plasma skimming have been observed in the vessels of the rabbit’s ear, one in which CONTRAOTION OF BLOOD VESSELS 115 the vessels contain a circulating plasma and the other in which there is no circulation. Venous and capillary pulsation have been seen in one plexus or another at all times during the new growth of vessels, particularly in vessels which are either short circuits between those which carry the main flow of blood, or blindending tubes. A very slight pulse is usually present in all young capillaries, but it is barely perceptible to the eye except when the rate of flow diminishes. I n the older tissue, however, a well-defined capillary pulsation is extremely rare, except when the rate of flow is very rapid or very slow, and even then it is present in only a few vessels. One small plexus of blood vessels, containing a single pulsating capillary, was studied carefully in order to determine the cause of this pulsation. The plexus contained two capillaries which emptied close together into a very large vein, in which the flow was even and constant. When the circulation throughout the plexus became slow, one of these capillaries pulsated while the other did not. It was seen that these two capillaries were each supplied by a different arteriole, one of which supplied several other capillaries with blood, while the second arteriole had no other capillary branchings. I n the latter arteriole the rate of flow was diminished, and it was in the capillary connected with it that the pulsation was observed. Blood cells were seen to enter the large vein from this capillary in an interrupted stream, a few cells with each beat of the heart. The flow through the entire vein was perfectly stead-y and it seemed probable that the pulsation in this particular case was present in the one capillary on account of the short connection between the arteriole and vein, and absent in the other on account of the greater number of capillaries which its arteriole supplied. As for the venous pulse, it may be due to a transmission of the arterial pulse to the veins, or possibly to the contractions of the right auricle. It is difficult to explain the general pulsation which may occur in veins and capillaries when the circulation is extremely fast, as, for example, when the ear 116 J. C. SANDISON is heated to 38°C. or above. At such a time the arterial wall is distended slightly at each beat of the heart, the arterioles are distinctly narrowed, the capillaries and venules are slightly narrow, and the rate of blood flow in the large veins is almost equal to that in the artery. While the circulation in a capillary bed is almost entirely regulated by the action of muscle cells on arterial vessels supplying it, it has been found that the flow may be diminished or even stopped by a single leukocyte plugging a narrow vessel. This occurs frequently, but is of minor importance, since it is always temporary. One of the most favorable places for such plugging is at the origin of the small arterioles Cap Artery Fig. 3 Camera-lucida drawiiig of a precapillary braiich o f ail artery. The artery has a double layer of muscle cells (Musc.) ; the entrance t o the preeapillarv is almost obliterated by the bulging eiidothelial iiucleus (End.NucZ.) . hdveiititial cell (Adv.) ; capillary (Cap.). X 412. from their arteries. Normally, this region is constricted partly on account of the bulging of endothelial cells into the lumen. Such a bulging in a capillary is shown in figure 3. At times the constriction is too great to permit the passage of the leukocytes, though the more elastic erythrocytes map pass quite readily. Unless the force of the blood stream (always variable) is sufficient to push the obstructing cell onward, the latter may stop the circulation in the capillaries fed by the arteriole for varying lengths of time-sometimes f o r several minutes. One such arteriole was watched and the following was observed: With a rapid rate of flow, a condition which was always caused by a dilatation of the artery, both the erythrocytes and the leukocytes were forced through CONTRACTION OF BLOOD VESSELS 117 the narrow lumen in the form of an unbroken stream, even though they were enormously distorted in passing. With a moderate rate of flow the erythrocytes passed through easily, though again distorted, but the leukocytes went through the constriction in a jerking manner, apparently due to the effect of the systolic waves upon them, and each one plugged the vessel for a certain length of time. Occasionally the leukocytes' own ameboid activity would assist their passage. The time required for the passage of a leukocyte through such a constriction depended upon the activity (blood pressure) of the general circulation, being greater with a feeble blood stream. At periods of a steady, rapid rate of flow, the number of leukocytes which passed through this arteriole was an average of forty per minute. REACTION O F BLOOD VESSELS TO TEMPERATURE CHANGES I n addition to the factors just described, which change the rate of flow and the amount of blood distributed through the vascular system, one other phenomenon has been studied in this connection, namely, the reaction of vessels to temperature changes (figs. 4 and 5). The higher temperatures were produced by an ordinary 60-watt electric-light bulb, the degree of heat being regulated by the distance of the bulb from the ear. The temperature was measured by placing a thermometer a few millimeters above that p a r t of the ear which received the greatest amount of heat. The vessels were studied a t three different temperatures: 37"C., 26" to 32"C., and 20°C. (produced by placing sponges dipped in ice water directly 011 the surface of the chamber). VCThile the heat was being applied, the circulation gradually became more regular and faster, until, by the time the maximum of 37" was reached, it was quite regular in rate of flow and the speed was exceedingly rapid, being almost as fast in the veins as in the arteries. I n addition t o the rapidity of flow, a general pulsation of the vessels could be seen. The rhythmical contractions previously described now occurred only at very long intervals and lasted for a very brief period 118 J. 0. SANDISON of time. After the light bulb was removed and as soon as the ear became accustomed once more to room temperature, the circulation continued as it did previous t o the experiment. The sticking of leukocytes to the walls of capillaries and their emigration through the vessel walls, following heating of the ear to 37 C., has already been described ( Sandison, '31). When the ice packs were applied, the branches of the larger arteries contracted completely, and all circulation in the chamber stopped. Very occasionally the arteries would open slightly and permit a sluggish flow of blood, but this partial dilatation had very little eEect upon the capillary circulation. The exact point on the arteries where this marked contraction ended varied in all of them, but it rarely extended to the arterioles, most of which were slightly dilated. When the ear was brought back to room temperature, the circulation again returned to its normal condition. The specific reaction of the different types of vessels during these experiments may be followed in figures 4 and 5. Here it is seen that the main vessels concerned in the regulation of the blood flow are the artery and arteriole. At 20°C., the artery, by its contraction, is alone responsible for the stasis which develops, the arterioles are incompletely dilated in the region of their muscle cells, while all other vessels are wider than at any other temperature. The rhythmic contraction of the arteriole disappears. The small vessels at 32°C. are on the whole narrower than at 20°C., and the rhythmic contraction of the arterial vessels is more regular at this temperature. At 37"C., the capillaries, the arterioles, and the arteries are smaller than at any other temperature; the veins, though larger than at 32"C., are smaller than at 20°C. O Fig. 4 Camera-lucida drawings, showing changes in the caliber of all types of vessels with three different degrees of temperature. The insert a t the upper right corner shows the parts of the plexus from which the segments of different vessels shown in figures 4 and 5 were taken. A , arteriole; ( H , origin of arteriole A ) ; B, a precapillary; C, a loop of the prepostcapillary; D , a venule; Dil., greatest degree of dilatation ; Con., greatest degree of coiltraction ; N o Con., n o contraction; a and a l , flame group of muscle cells; b and b l , the same adventitial cell. X 310. 119 :ONTRACTION OF BLOOD VESSELS Dil. 1 Con. D i I. c e7 Con. 1 B Arteriole D i I. hrtrriolr cap I'reenp 32T. No Con. / A f 0 A B 20°C. Figure 1 c D 120 J. C . SANDISON REACTION O F T H E BLOOD VESSELS TO ADRENALINE AND HISTAMINE For these experiments a preparation was used containing adrenaline, 9/20 grain ; chloretone, 24 grains, and physiological salt solution, 1 fluid ounce. For intravenous injection a dilution of 1: 100,000 was employed. Observations of the blood vessels in the transparent chamber were made during the injection of the drug into a vein of the opposite ear, and a region among these vessels was selected where an artery of a caliber of over 125 v, with its arterioles, capillaries, venules, and veins could be watched. This artery had at least three layers of muscle cells around it. Before the injec- Art E Vein F Fig. 5 Camera-lucitla sketch, showing changes in calibcr a t diff ereiit tempcratures of three other vessels of the same plexus shown i n the inset figure 4. E , a n artery having two layers of muscle; P’, a vein; G , the more proximal portion of the artery; E, point beyond whieli coiitraetioii did iiot occur at 2 0 ”. x 206. tion was begun, the normal changes in caliber of this vessel and of its arteriole branchings mere noted, and they coiiformed to the changes whicli hare been previously described. At no time did this artery constrict more than one-half of its fully dilated caliber and the rhytlim of its contraction was similar to that which has also been previously described for arteries in this chamber. Surrounding the wall of the proximal half of the visible portion of this large artery were numerous macrophages which contained a dark yellow-brown pigment. The vessel had slight local contractions here and there along its wall. The injection needle was quickly thrust into the vein with one movement. Almost immediately the arterial vessels com CONTRACTION O F BLOOD VESSELS 121 stricted slightly more than normal, and in a few seconds they dilated fully. This is the usual response to any disturbance to the animal. Then, after one minute, a t the end of which time these vessels were still dilated, a slow injection of the adrenaline was begun. The large artery began constricting one and one-half minutes after 0.3 cc. of the 1:100,000 solution had entered the vein. Injection was then stopped. A few seconds later the large artery constricted to about 25 p in caliber (one-sixth its dilated caliber) along its proximal half. The degree of constriction was less along the remainder of its course, being less marked the more peripherally one followed it. The normal, locally contracted regions were the points of greatest constriction in any one segment of the vessel. The lumen, even though greatly constricted by contraction of the muscle cells which were much thicker than normal, widened slightly with each beat of the heart. The arterioles were greatly constricted along most of their course, but they showed only a partial contraction near their capillary terminations, even though they were surrounded in that region by a single layer of muscle cells (fig. 6). They were most constricted a t the point where they took origin from the large artery-a point where they are normally narrower (fig. 3 ) . The venules also narrowed, but to a slight extent only. The capillaries were apparently unaffected, except for the usual very slight changes which normally accompany changes in blood pressure, i.e., a slight dilatation with decreased rate of blood flow. The flow of blood in the capillary bed varied in different capillaries from a complete stop to a moderate rate, depending upon their proximity to an arteriole. In most of the main pathways which lie between the arteriole and the venule a slow circulation prevailed. One interesting observation during the contraction of the large artery was the effect upon the pigmented macrophages which surrounded a part of this vessel. They were apparently unchanged in regard to their position-a wide clear space between them and the muscle cells of the vessel wall being quite evident, whereas previous to the time of injection they had lain directly upon these muscle cells. THE A N A T O M I C A L RECORD, VOL. 54, N O . 1 122 J. C. SANDISON The constriction period in all vessels was not over two minutes, and one and two-thirds minutes after the injection was stopped the arterial vessels began to dilate; twenty seconds later, the dilatation was almost complete. At this moment a second injection was begun, the needle having been kept in place, and 1.2 cc. of the adrenaline solution was steadily emptied into the vein over a period of four minutes. NC t Fig. 6 Camera-lucida drawing, showiiig effect of ail iutraveiious injectioii of adreiialiiie chloride (1: 100,000). The arteriole contracts, while the capillaries aiid veiiules are uiiaff ected. Dotted line indicates degree and limit of contraction. Eiidothelial nuclei dotted, adventitial cells cross-hatched, smooth-muscle clear ovals. N.C., 110 coiitractioii beyond this point. X 316. One and one-half minutes from the beginning of this second injection, after 0.3 cc. had again entered the circulation, there was a repetition of the change in caliber of the vessels similar to that noted after the first injection. At the end of two minutes, dilatation was not complete, but there was a considerable widening of the arterial vessels. The injection was continued, and one-half minute following this incomplete dilatation a constriction of the vessels again occurred, but to a much less degree than the one which just preceded it. The CONTRACTION O F BLOOD VESSELS 123 vessels remained in this state of partial constriction for one and one-half minutes after the injection, at which time they dilated and this dilatation, which was general, lasted a t least one-half hour. The effect of this arterial dilatation on the capillary circulation was marked and brought about a great increase in the rate and amount of flow through all vessels with the establishment of circulation in capillaries which were previously open but non-circulating. Under the action of a more dilute solution of adrenaline (0.3 cc. of 1: 500,000) the capillaries gave the same response, but there was less of the primary slowing of the capillary circulation, partly on account of a lesser contraction of the arterial vessels. When 2 minims of 1: 1000 solution were injected subcutaneously, the vessels responded as they did with the intravenous injection, except that the contraction of arteries and arterioles was prolonged for seven minutes o r more, and the return of the normal rhythm of these vessels appeared much later. Local application gives such a picture as shown in figure 7. The effect of histamine upon the blood vessels was also observed. The same method of study as that used with adrenaline was employed, except that only one dilution (1:100,000) was used, and only the intravenous route of injection was chosen. The action of 0.004 mg. of this drug resulted in dilatation of arterioles and arteries with almost complete stasis throughout the vessels of the chamber for over two hours. The greatest degree of dilatation occurred in the arterioles, since they widened to twice their usual diameter. The capillaries were unchanged in caliber, except for the usual slight dilatation following lack of flow through them, and all of the previously non-circulating, wide-open capillaries were filled almost to capacity with blood in stasis. The very narrow capillaries, which are the retracting or the new-growing vessels, were observed particularly for dilatation, but they also were unchanged. Frequent reversals of flow in all vessels were noticed. The next day, eighteen hours later, cc. of adrenaline was administered subcutaneously in + 124 J. C. SANDISON the abdominal region, and all of the arterial vessels, which had dilated with the injection of histamine, then contracted. The results, therefore, of the action of these two drugs on the vessels of the rabbit’s ear show that the various responses are chiefly confined to the vessels which are surrounded with muscle cells. With dilute intraveous injections, adrenaline causes a fleeting constriction of all arterial vessels in the Capillaries Arteriole 1 2 Fig. 7 Camera-lucida drawing, showing degree and limit of actioii of a local iiijectioii of 1: 1000 adreiialiiie chloride. M , muscle cell. 1, preceding, aiid 2, folIowiiig injection. X 310. chamber with diminished capillary circulation, which action is quickly followed by an arterial dilatation, accompanied by a much more rapid capillary flow than that usually present in the normal circulation. Histamine causes a still greater diminution of the capillary circulation, and dilatation of all the peripheral arteries and arterioles with the strength of solution used. Neither drug acts, apparently, on naked endothelium. CONTRACTION O F BLOOD VESSELS 125 SUMMARY hlicroscopic observations have been made on new blood vessels which have grown into a transparent chamber introduced into the rabbit’s ear, and which have persisted for from two to four and one-half months, with the following results : The local control of blood flow in this newly formed tissue appears to reside in the smooth-muscle cell on the arteriole. Adventitial (‘ Rouget ’) cells are present in large numbers, but do not appear to contract. Capillaries proper, with or without perithelial (‘Rouget ’) cells, have such a limited power of contractility that they seem to play no significant part in the control of circulation. While their caliber manifests changes, the changes seem t o be passive rather than active, and brought about chiefly by changes in pressure both within and without, coupled with a certain degree of elasticity of endothelium. However, in the persistent absence of blood flow through a capillary it may gradually narrow until its lumen may permanently disappear -rather a retrogression in growth than contraction. Nothing was seen which could be interpreted as active contraction of any of the veins or venules under observation. Application of heat to the ear caused an extremely rapid flow of blood, the arteries, veins, and capillaries maintaining a uniform caliber. Cold applications caused persistent contraction of larger arteries with sluggish flow and slight widening of small arterioles, capillaries, and veins. With both heat and cold there was a marked degree of sticking of leukocytes to the walls of veins and venous capillaries, and, in the case of heat, extensive emigration of leukocytes through the endothelial wall. Injection of adrenaline was followed by marked contraction of the arteries and arterioles at places where they were obviously provided with smooth-muscle cells, while capillaries and venules showed only slight, and apparently passive, changes in caliber. Contraction of arterioles was followed, after a few minutes, by a half-hour’s dilatation. 126 J. C. SANDISON Intravenous injection of histamine produced relaxation and widening of the small arteries and arterioles, coupled with diminution in blood flow. Capillaries and small veins showed no appreciable change in caliber. Many of the interesting pictures to be seen in watching the circulation are described, most interesting of which are perhaps ‘plasma skimming’ (Krogh), platelet ‘ skimming, ’ and leukocyte ‘skimming. ’ Whether the new vessels under observation were supplied with nerves was not determined. LITERATURE CITED CLARK,ELIOTR. 1932 A iiew method f o r the microscopic study of cells and tissues i n the living mammal. I n t . Clinics, vol. 1, series 42, p. 301. LINTONCLARK 1925 A. The development of CLARK,ELIOTR., AND ELEANOR adveiititial (Rouget) cells o n the blood capillaries of amphibian larvae. Am. J. Anat., vol. 35, no. 2. B. The relation of Rouget cells to capillary contractility. Am. J. Anat., vol. 35, 110. 2, p. 239. 1932 Observations on living preformed blood vessels as seen in a trailsparent chamber inserted into the rabbit’s ear. Am. J. Anat., vol. 49, no. 3, p. 441. CLARK,ELIOTR., H. T. KIRBY-SMITH, R. 0. REX, AND R. G. WILLIAMS 1930. 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